Fast mechanisms for the formation of new plate boundaries

We demonstrate the important role played by non-linear feedback in promoting the fast breakup of the continental lithosphere and the formation of new plate boundaries. We compare the difference in fluid-dynamic and elasto-visco-plastic approaches and emphasize the advection of stresses in finite-element models with large strain Lagrangian formulation. Two types of instabilities were found at multiple time-length scales ranging from 100 years and km scale to 0.1 Myr and 100 km scale. One mechanism relies on the thermo-mechanical elasto-plastic energy conversion, and the other stems from the void-volatile interaction. Elasticity takes on a guiding role in the propagation of shear zones, closely followed by a thermal wave, which is again followed by a wave of volatiles. This last mechanism consolidates the fault zones and establishes the plate boundary for a geological time-scale. Using a fully coupled thermal-mechanical approach, we obtain for the first time a two-dimensional solution, which shows that the constant velocity boundary conditions can lead to episodic avalanche-type tectonic phases within <0.1 Myr. (C) 2000 Elsevier Science B.V. All rights reserved.